1. Field of the Invention
The disclosures herein relate to an imaging apparatus that is provided with a light transmissive filter having a plurality of polarizing filters or color separation filters arranged therein, and that produces image signals by imaging an object.
2. Description of the Related Art
In digital cameras or the like, an imaging apparatus takes an image of an object to produce image signals, and may separate the image signals into image data of different wavelength bands. In other examples, an imaging apparatus takes an image of an object to produce image signals, and may separate the image signals into image data of different polarization components. This may be performed for the purpose of enhancing the contrast of the imaged object by removing unnecessary polarization components. Such imaging apparatuses may use a light receiving device array in which light receiving devices of the same type are arranged, and may separate incoming light into light components having different polarization directions or different wavelength bands.
For example, an area-divided-type filter that has its entire area divided into plural types, each allowing the passage of light having a different characteristic, may be disposed in front of a light receiving device array such as a CCD (Charge Coupled Device), a CMOS (Complementary Metal Oxide Semiconductor), or the like. Signal processing is then performed on image signal data output from the light receiving devices. With this arrangement, a plurality of image signals are obtained as if light receiving devices of different types corresponding to light transmissive filters of respective, different characteristics were provided.
In one example, a color filter may be disposed in front of a light receiving device array such as a CCD. This color filter may include spectral filters (hereinafter referred to as “spectral filter sections”) having different light transmission wavelength bands disposed in a predetermined arrangement pattern as in the case of a color separation filter (i.e., area-divided spectral filter), in which areas are divided into R (red), G (green), and B (blue). The light receiving device array is used to produce image signal data of respective colors. Such a configuration is disclosed in Japanese Patent Application Publication No. 2007-086720, for example.
In another example, a polarizing filter may be disposed in front of a light receiving device array such as a CCD. This polarizing filter may be an area-divided polarizing filter that includes plural polarizing filters (hereinafter referred to as “polarizing filter sections”) having different polarization directions disposed in a predetermined arrangement pattern. A single image signal obtained by imaging an object is separated according to polarization directions to produce plural image signals. Such a configuration is disclosed in Japanese Patent No. 3771054, for example.
The imaging apparatuses as described above have the following problems.
In such imaging apparatuses, light received by a single light receiving device corresponding to a single pixel of an image needs to have passed only through one of the plural light transmissive filters (hereinafter referred to as “light transmissive filter sections”). To this end, the shape and size of each light receiving device need to match the shape and size of each light transmissive filter section if the light receiving devices are provided in one-to-one correspondence to the light transmissive filter sections.
In an imaging apparatus, a light transmissive filter provided as a separate unit is attached by an adhesive agent or the like to the front face of a light receiving device array such as a COD or CMOS. Accordingly, the provision of filter sections having shapes and sizes that match those of the light receiving devices alone is not sufficient. There is an additional requirement that the light transmissive filter sections need to be accurately aligned with the light receiving array.
If the light transmissive filter sections are displaced relative to the light receiving devices, a single light receiving device may receive light through plural polarizing filter sections having different polarization characteristics. The image signal data output from this light receiving device is different from what is intended as polarized image data. Polarized image data may not be obtained at all depending on the ratio of mixing of lights.
If the light transmissive filter is displaced by rotation relative to the light receiving devices, such a displacement may be regarded as a parallel displacement in a small area of interest for a small rotation angle. In the same manner as described above, such an arrangement gives rise to a problem in that polarization information may not be properly obtained.
These problems that result from the use of a polarizing filter in which plural polarizing filter sections are arranged as an array also occur in the case of a spectral filter in which spectral filter sections are arranged as an array. If the position of a color separation filter is misaligned with the light receiving devices, image signal data produced by a light receiving device ends up being an average of image signals corresponding to lights passing through the respective RGB color separation filters. This gives rise to a problem in that color image information is not properly obtained.
Accordingly, there may be a need for an imaging apparatus that can reproduce image signal data corresponding to respective light transmissive filter sections even when the accuracy of alignment of the light transmissive filter disposed in front of light receiving devices is not sufficient.